1. Field of the Invention
The present invention generally relates to a light guide plate and a surface light source employing such light guide plate.
2. Description of Related Art
Recently, liquid crystal display devices have been remarkably improved, and their market has been steadily growing because they can save installation space by virtue of their thickness, and they can also save power.
Liquid crystal displays commonly use a surface light source to provide illumination. The surface light source includes a light guide plate having a shape of a planar plate or a wedge. The light guide plate distributes light from a substantially linear source, such as a cold cathode fluorescent lamp (CCFL), to provide substantially planar illumination to the LCD.
As is well known, the light guide plate is provided for the distribution of light from the light source over an area much larger than the light source, and more particularly, substantially over an entire output surface area of the light guide plate. In operation, light beams typically enter the light guide plate along an edge surface, and may propagate between a bottom surface and the output surface toward an opposing end surface of the light guide plate by total internal reflection, or may also be output through the output surface directly. Further, the bottom surface includes structures such as dots formed on or facets cut in the bottom surface and arranged in a pattern. The light beams encountering one of these structures are diffusely or specularly reflected, so that they are emitted through the output surface.
Unfortunately, in operation, some light beams are reflected by the light incident surface and cannot enter the light guide plate, or are reflected by the light-emitting surface and cannot be output to give an illumination. Moreover, some light beams exit from the side surfaces and the bottom surface of the light guide plate, all of which results in losses of light.
In order to prevent the light beams that exit the bottom surface from being lost, it is know to provide a reflector adjacent to the bottom surface to reflect these light beams back into the light guide plate. However, once these light beams have exited the light guide plate, it is difficult for them to reenter the light guide plate. In order to prevent the light beams from exiting the side surfaces, it is common to provide reflectors supported by a frame member on the side surfaces to reflect the light beams back into the light guide plate, but this results in more parts in the display system and a weightier overall display. Another design is to secure the reflectors directly to the side surfaces using adhesive, but the reflectors are easily stripped in transportation or other operations.